1. Field of the Invention
This invention relates to a preparation process of an alkali metal salt of a phosphoric ester, more specifically to a process for the advantageous preparation of an alkali metal salt of a phosphoric diester by reacting a monoalkali metal salt of a phosphoric monoester and an epoxy compound with good selectivity.
2. Description of the Prior Art
Phosphoric esters are now employed in a wide variety of fields, as detergents, textile conditioners, emulsifiers, rust inhibitors, liquid ion-exchangers, medicaments, etc. Extensive investigations have been being carried out with a view toward introducing one or more structural moieties of different functions in such phosphoric esters while maintaining their inherent functions so that their application field would be expanded further. For example, investigations are now under way to introduce a polymerizable group or a hydrocarbonyl group, each of which contains one or more hetero atoms, e.g., halogen and/or nitrogen atoms so that monomers having phosphoric ester structures and phosphoric esters, each, having a quaternary ammonium salt in the same molecule, such as phospholipids are obtained.
As one of processes for obtaining such compounds, it has been known to subject a phosphoric ester to phosphorochloridate by means of a chlorinating agent such as thionyl chloride or to prepare a phosphoric ester having a phosphorochloridate structure and then to react it with its corresponding organohydroxy compound (see, for example, Japanese Patent Publication No. 30768/1980). The above process is however accompanied by byproduction of hydrochloric gas. Accordingly, it involves difficulties in the treatment of the byproduct, maintenance of the work environment and the like and is hence not suitable as an industrial preparation process.
As another process, may be mentioned to makes use of the reaction between the phosphoric acid group, which each phosphoric ester has, and an epoxy compound. According to this process, the intended compound can be easily obtained from an epoxy compound containing a polymerizable groups or nitrogen atoms and a phosphoric ester. This process is thus the most suitable process for the industrial preparation of such materials. When this process is however applied to a phosphoric monoester, the process produces not only the intended compound, i.e., the corresponding phosphoric diester in which only one hydrocarbyl group having a specific function is selectively introduced in the phosphoric monoester, but also the corresponding phosphoric triester which contains an additional hydrocarbyl group of the same kind introduced therein. It was hence difficult to obtain the intended compound, for example, a polymerizable monomer having surface activity or an analogous monomer in a purified form and with a good yield.